by Rob Dunn
Binford and his critics agreed upon some parts of the story of the origins of agriculture. It was known that long before agriculture was practiced for sustenance, it was done more casually. Someone might find a vine he or she liked and sink it into the ground by their house. They might uproot a favorite tree and replant it. They might even more actively cultivate a few things here and there. That was the extent of it perhaps for the simple reason that harvesting food from the forest was easier. It did not require much time, just four to six hours a day, to collect enough food for a family.4 The rest of their time was leisure. On this point, there is little disagreement. The average day of a hunter-gatherer was composed of a little work and lots of time for art, dance, and, one presumes, sitting around and telling stories. The disagreement begins in terms of what happened next.
Imagine for a moment the scenario as Binford saw it. You live in a small community of a larger tribe that over generations becomes larger and larger. As it does, food starts to become scarce around the village, particularly as movement becomes more difficult. Favorite plants disappear first. Pests build up. Fleas live in each house, lice too, and other animals. In times gone by you might have moved your village. Perhaps you would have moved it sooner in some places, such as the tropics, than others, but eventually, regardless of where you were, you moved it. Innumerable villages in the Amazon, as elsewhere, roamed like locusts. In the Amazon, it takes about fifteen years for the fleas, lice, bats, and other realities of jungle life to build up in a group of houses beyond livable densities. So it was that most Amazonian hunter-gatherers, just like those in tropical Africa or Asia, once moved about every fifteen years. But at some point you could not move anymore. The forest in every direction was already occupied. So you stayed, and as you did, the inevitable sank in around you. Pathogens and their diseases grew more common, and the food on the trees and in nests and caves grew less. It happened, perhaps, in a bad year, when there was not enough to eat in the other villages either. In such years, many would have died. They would have rocked in their hammocks, hungry and flea-bitten. Those who survived may have been the few who still had some food, food planted near their houses, not yet domestic crops, but crops that might be domesticated. They ate what grew and, if they could, planted more. Whole villages died, but in your village the few plants took. On those first crops—the near-cold embers of humanity—you and a few others survived, tending each stem and seed carefully, the way one might tend a fire in the dark, with the knowledge that each seed must be passed on, back into the soil, as they have been until today.
Binford imagined that at least some of our ancestors in the Americas and elsewhere turned to agriculture out of such desperation. He imagined that as populations grew too dense, many individuals died from starvation. Perhaps only a few individuals or families would have farmed enough, quickly enough, to survive. In Binford’s view, agriculture was, at least sometimes, and maybe even usually, a desperate act. From that act arose societies that had not invented agriculture, but rather had been conquered by it. The first crops would have begun, almost by definition, as too rare to sustain anyone, or nearly so. They would have been difficult and tedious. Any variants of genes in humans that made it easier to live off those crops, to digest them, for example, would have been favored. So it was, Binford imagined, that their cultures and maybe, just maybe, their genes, came to revolve around agriculture. Communities became sedentary and their diets grew worse. In agriculture, Binford saw a bane of humanity. But by the time humans began to write, we had committed ourselves irrevocably to that lifestyle. If correct, this view would have many consequences for who we are and how we live now. Among the consequences is that crops are inevitable, permanent, and problematic. Crops allowed a few lucky peoples to increase in density beyond what had ever been possible before, but whereas once they had depended on thousands of species as our mutualists, they came to depend on just a few, and in some places, just one. They and, by descent, we became linked not just to food production in general, but even to individual kinds of crops. In the Amazon, it was peanuts and yucca (Cassava manihot). Elsewhere this tragic play would be reenacted with different species, but with actors and roles that were, to Binford, eerily the same.
Binford’s view of agriculture as a kind of postapocalyptic sustainment was attacked and criticized by other anthropologists for years. It conflicted with the story we tell about ourselves in which we are innovative, successful, and in control of our fate. With time, Binford went on to do other things and think about other questions. He had, he thought, good evidence for his theory, but some potsherds and bones were not enough, and so his idea lay fallow, until now.
Binford’s view of history and agriculture may not be the rule everywhere. Recently, the evidence seems to be gathering that it is the rule, or at least the story, some places. A telltale gene, a gene that points to what happened to humans at the dawn of agriculture and how we changed, has now been discovered. These genes and their variants prove how important the domestication of plants and animals was to our survival, if not in every case, then at least sometimes. They also make clear what Binford could only allude to, the extent of the domestication of humans.
The story of these genes begins with the aurochs (Bos primigenius), the ancestor of modern cows. Aurochsen evolved in northern Africa and southern Asia at a time when grasslands had spread across much of those continents and tropical forests had shrunk back toward the equator. These beasts fed on the new, more bountiful kinds of grasses. They were just one of many kinds of cow-like animals that evolved during this time, including bison (Bison bison), banteng (Bos javanicus), and others. Yet they would be the chosen one, one of our chosen ones. Each adult aurochs (plural aurochsen) stood more than six feet tall at the shoulder. Aurochsen had the shape of a cow, but were closer in size to a small elephant. Oversized, they spread across the expanding grasses like aphids over the canopies of trees. Their big teeth evolved to clip the grass toward its base and grind it. Inside their stomachs was a storm of life—bacteria, archaea, even protists—which aided them in digesting their food. Without these, their own partners, they would not have survived.
Aurochsen prospered on the great miles of grass. Yet, as much as the green buds were sustaining to the aurochsen, such succor was elusive for humans. Humans never evolved the ability to eat grass. We can chew it, but the cellulose and lignin out of which it is made passes through us, untouched by our digestion. Only the seeds, the so-called grains, satisfy us, and so, at least initially, in looking out at the fields of green, our ancestors were parched mariners at sea, damp and still thirsty, surrounded by food and still hungry. Yet each food must be tried before it can be abandoned, so our ancestors would have grabbed handfuls of grass and stuffed it into their mouths. They would have chewed and hoped. We failed, precisely where the aurochsen seemed to succeed.
Success though, just like failure, has its limits, its breaking points. Eventually, the aurochsen ran out of new grasslands to colonize. Grass stopped at the forest edge, and so did the aurochsen. Limited by such natural boundaries, they seemed as successful as they ever would be. Then, on some dark path, an aurochs met a human. A deal was about to be made. In the real story of temptation and consequence, the forbidden and consequential fruit was not an apple, but instead an aurochs’s hairy teat.
In the beginning, the relationship was awkward. There was fumbling and a kind of inescapable nakedness. Initially, milking would have been difficult. Even today, considerable effort goes into convincing cows to “let down their milk.” As Juliet Clutton-Brock puts it in her book on the natural history of domesticated animals, “The cow must be quiet, relaxed and totally familiar with the milker . . . her calf must be present, or a substitute that she identifies with the calf . . . and it is often necessary to stimulate the genital area before the milk-ejection reflex will initiate secretion.”5 Awkward indeed. Yet from that first human beneath the cow and others like him would descend much (though importantly not all) of future humanity.
> Just as with the origins of agriculture more generally, the details of this beginning were long speculated upon, but difficult to know. Many archaeologists and cultural anthropologists imagined that such domestication events, be they of cows or crops, happened at the margins of an already successful society. They believed the story as it had been laid out in textbooks. The domestication of the aurochs was yet another manifestation of our power for innovation and the control of nature, a kind of nascent science and technology. In retrospect, our ability to shrink wild animals and make them live with us seems near magical. We tamed the cow, but also, later, horses, goats, cats, and dogs too. We did it one coupling or slaughter at a time. It is easy to get caught up in this godlike act of transformation. It turns out, though, that the aurochsen were not the only ones that were transformed. They changed us too, though no one knew that until very recently. They did not “intend to” and yet the result, from evolution’s unconscious perspective, is the same as if they did, as if they wanted to be ours and us theirs. Even Leigh Binford, who thought that agriculture was the result of survival through hard times, did not imagine how hard the times might be, nor how much they would change who we are.
In the last five years, the modern tools of genetics have allowed us to ask not just how species are related, but also when particular genetic variants and the abilities associated with them evolved and, once they evolved, how quickly they became common. Most new genes—mutant genes—disappear immediately. Their bearers die. A few new genes persist, and those that persist meet one of several fates. They may persist for a while and then disappear. They may increase, slowly, in their commonness because of some modest advantage they confer. What is also possible, but unlikely, is that once a new gene arises, it becomes nearly immediately universal. The only way for that to happen is if its bearer mates with nearly everyone, or if nearly everyone missing the gene dies. Geneticists euphemistically call such scenarios “selective sweeps,” which sounds more like a good hockey series than a period during which individuals without a certain trait fail.
New genetic methods have allowed scientists to reconstruct the stories of the aurochs and of humans separately and then to weave those two narratives together. The story of the origin of the cow from the aurochs begins around 9,000 years ago, somewhere in the Near East, where aurochsen began to come into human settlements. Perhaps that is where they found the sweetest grass. Perhaps that is where they were safest from predators. It is difficult, maybe impossible, to know. Yet, however they initially came to us, whether easily or stomping and kicking, in relatively few generations they were tamed. From this and subsequent points of contact, the aurochsen would spread with humans into new areas, including much of Europe but also new habitats in Asia. They spread into habitats as humans cleared them. They spread beyond their native range, and as they did they became more and more different from those individuals untended by humans, those wild aurochsen that with time would eventually disappear, outcompeted by their newly more domestic kin who from that first day on would always have the help of humans. With humans, the aurochs did far better than it might have done otherwise. It succeeded even as other herbivores, predators, and harvested plants around it were becoming extinct.
While a suite of genes associated with smaller bodies and docility came to be favored in aurochsen as they interacted with humans, a unique set of traits also began to be favored in humans themselves. The traits favored were those associated with lactase persistence (the ability to digest milk as an adult). Adult dogs cannot digest milk, nor can adult cows, pigs, monkeys, rats, or any other mammals. Even adult cats, who we so readily give a bowl of cow’s milk, appear to lack the gene to effectively break lactose down. Milk is baby food, or at least it is for all mammals except some modern humans. In order to digest milk as adults, humans had to evolve the ability to continue to produce lactase as adults. Lactase is the enzyme that breaks down the lactose in milk and makes it useful. Our ancestors, it is very clear, could not digest milk as adults. Cavemen and -women, if they drank milk, would have had diarrhea and gas. Perhaps they could have obtained some nutrients from the milk, but not many and if they were already sick, milk and its consequent diarrhea might have even made them sicker. Yet today, most peoples of western European descent, which is to say those people who descended from the first cow tenders, can digest milk as adults. In other words, as aurochsen changed genetically during domestication, so did humans. As we did, we became domesticated too. Once we grew dense enough to need to depend on cows, we could not go back to our hunter-gatherer days. Our lifestyles changed, permanently, as did our genes. We were no longer wild.
Several years ago scientists identified the mutation that is associated in Europeans with the ability to drink milk as adults. (The mutation leads to the production of lactase or, more specifically, lactase-phlorizin hydrolase.) With this sequence decoded, they could study when it arose and how quickly it spread among populations once it had arisen. The first answer came more quickly. The mutant form of the gene for digesting milk in adulthood arose 9,000 to 10,000 years ago, just as archaeological evidence and evidence from the genes of cows suggest that humans and aurochsen came together for the first time.6 Here, in other words, was a genetic artifact left to tell the story of the earliest days of humans and cows, a marker whose presence in a person would speak to the story of their descent.
Just how fast the gene spread took longer to discern. It required more time and technology, but the question eventually yielded to scientific persistence, more blood samples, and hours in the lab looking over computer printouts of the As, Ts, Cs, and Gs of the genetic code. The short answer was “quickly.” In the tribes of our ancestors where cows were first domesticated, those individuals—the majority—who could not digest milk as adults suffered and died. The few who could digest it suffered less and survived. Just as Leigh Binford had long ago argued about agriculture more generally, the dawn of our cattle farming was not some happy bursting forth of innovation, but a more difficult and permanent contract. One might then see that first man who extracted milk from a cow as a kind of early hero, evidence of the way that even in the worst of situations, humans will rise and persevere. Because of his lineage, we abandoned our old mutualists, the many kinds of wild plants and animals we once collected, for the fewer we could grow and farm. As we did, we become dependent on our new partners—our crops. We would continue to change, but only inasmuch as we would replace one species with another, wheat for cows, or sorghum for wheat. Since that moment, we have survived by dint of our crops and cattle, and by them alone.
We tend to think of ourselves as special, and so we call those circumstances in which we come to depend on another species domestication. In truth, though, so long as we and our domesticates both produce more offspring together than we would apart, this is simply a new form of mutualism, one that like our other new interactions is simplified relative to the way we once lived. Humans with the genes for digesting lactose as adults fared better, and so did aurochsen with genes for being a little kinder to humans, for mating in captivity, and for producing more milk. Because of humans, the aurochsen with those genes were able to eat more grass, something they would never have found on their own. Although humans could not, without the aurochsen as intermediary, eat grass, they could make more grass by burning and cutting down forests. They could also reduce competition by killing the other animals that ate grass. Out of that first interaction came a mutual dependency. We depended and would continue to depend on the aurochsen to produce enough food to support the great densities to which our populations would rise. The aurochsen would depend on us to make ever more grass and to kill everything that might compete with or kill them in those new grasslands. Together we began to remake the world, not because we could, but because we had to. Once we entered this relationship, there was no turning back. With our help, the aurochsen that became cows outcompeted those that did not. Wild aurochsen are now extinct, as are nearly all of the big herbivores with which they once c
ompeted. We killed those competitors for the aurochsen and killed their predators too. Nor was it just the aurochsen’s competitors that would disappear. So too have most of the gatherers around the world, peoples pushed farther and farther into forests that are, each year, smaller and smaller, forests that have given way, by and large, to our aurochsen and our crops, the new mutualists.
Today, there are more than a billion descendants of aurochsen (cows) on Earth. We outnumber them, but we do not outweigh them, and so, depending on how you count, it is ambiguous whether they or we have had, in our coming together, more success. This reckoning is not quite right though, because the number that should be counted is not all humans and human lineages, but those specific lineages of humans with which cows have coevolved. That was long considered to be just Europeans. That was, it would turn out, wrong. Once again, studying the evolution of our differences would change our understanding not just of who we were but who we are.
Roughly ten years ago, the geneticist Sarah Tishkoff, now at the University of Pennsylvania, began to wonder how it was that the Masai, in East Africa, who tend cows by the thousand, drink milk. Tishkoff knew the story of Europeans and the aurochs. She also knew that in addition to Europeans, many other peoples around the world drink milk. The Masai and other cow-tending tribes spent and spend their days following their herds from place to place. In doing so, they drink great quantities of milk, as do many other pastoralists across Africa. In addition, it is known that cattle were domesticated independently in Africa (probably in the northeast) and spread south from that point of domestication. They appear to have spread to western and southern Africa and with them developed intricate cultures associated with cows and milk, cultures like that of the Masai. But the Masai and other tribes are obviously not the descendants of the Europeans who domesticated cows, and so it is difficult to understand how they could possibly have the gene necessary for drinking milk as adults.